The object of this invention is a water dealkylation catalyst for monoalkylated or polyalkylated aromatic hydrocarbons that has improved activity, selectivity and stability.
To satisfy the benzene demand, it is possible to dealkylate oil fractions that contain alkylated aromatic hydrocarbons. The treatment with water vapor makes it possible to effect this dealkylation while producing a gas having a high content of hydrogen.
Various processes of water dealkylation have been proposed that make use of catalysts including metals of the group VIII alone or associated with metals of other groups or with metal oxides.
In Haensel U.S. Pat. No. 2,436,923, there is described a catalytic process of demethylation of hydrocarbons, including alkyl aromatic hydrocarbons, by reaction with water or water vapor, in a water/hydrocarbon molar proportion of 2:1 to 12:1, in the presence of a catalyst comprising a metal of group VIII of an atomic number greater than 27 such as cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium and platinum.
In French Pat. No. 1,588,876, Rabinovich and Maslyanskii have described a dealkylation catalyst containing a noble metal of Group VIII and especially rhodium deposited on an alumina, either pure or doped with nickel or cobalt. A Japanese team of the Mitsubishi Corporation claims in French Pat. No. 2,169,875, the improvement of a rhodium catalyst on alumina by doping the carrier with cerium or uranium. U.S. Pat. Nos. 3,436,433 and 3,646,706 describe a catalyst that contains rhodium deposited on a chromealumina oxide doped with iron and potassium. In German Pat. No. 2,357,407 Girdler describes a water dealkylation process where the carrier of the catalyst, generally alumina, is advantageously exchanged with chromium oxide. In U.S. Pat. No. 4,013,734, Exxon has recently claimed rhodium on alumina dealkylation catalysts improved by doping the carrier with vanadium.
It is observed that in addition to the important part played by the metals of group VIII alone or associated with other metals or metal oxides, the catalyst carrier has an important function in the dealkylation reaction. The carrier must possess at the same time, activity which affects the rate of conversion, selectivity which affects the degradation of the products, and stability which provides extended operation without regeneration.